1. Field of the Invention
The present invention relates to an aqueous ink using a dispersible colorant and a water-soluble nonionic resin and/or an emulsion particle, an ink jet recording apparatus, an ink jet recording method, and an inkjet recorded image.
2. Related Background Art
The ink jet recording system adopts various working principles to produce images, letters or the like by ejecting fine ink droplets from nozzles onto a recording medium (paper or the like). It has been rapidly spreading in various uses because of their advantages of high speed, low noise, capacity of easily producing multi-color images, high flexibility of recorded patterns, and unnecessity of development/fixation. In particular, the full-color aqueous ink jet recording system techniques have recently made remarkable progress, and can now produce multi-color images which are by no means inferior to those by the conventional printing method or photography. It has been widely applied to the full-color image recording area, because of its capacity of producing printed matter at a lower cost than the conventional printing method or photography, when the number of copies is limited.
The ink jet recording apparatus and recording method using an aqueous ink have been improved to satisfy the requirements for improved recording characteristics, such as higher speed, finer images and full-color images. In general, the aqueous ink used for an ink jet recording apparatus is required to have the following performances; (1) even images of high resolution and high density can be obtained without occurrence of bleeding or fogging on paper, (2) the ink is ejected without being dried at the nozzle tips to prevent clogging there while keeping good ejection response and ejection stability, (3) the ink can be well fixed on paper, (4) the images have good weatherfastness, and (5) the images are stable for a long period of time. Especially, an ink that is dried and fixed rapidly and provides printing of high image-quality is being required with a recent increase in printing speed.
Colorants for use in the ink jet recording with an aqueous ink mainly include a dye and a pigment. Water-soluble dyes have hitherto been mainly used because of their handleability as aqueous inks and good color developability. More recently, however, essentially water-insoluble colorants, particularly pigments, have been extensively developed as colorants for aqueous inks for ink jet recording which can realize higher weatherfastness of produced images. For allowing a water-insoluble colorant, particularly pigment, to be used for aqueous inks for ink jet printing, it becomes necessary to stably disperse the colorant in water.
In this case, high dispersion stability has been generally achieved with the aid of a surfactant or polymeric dispersant (hereinafter, also referred to as dispersing resin). Further, another method has been proposed which chemically modifies the surface of a water-insoluble colorant (e.g., Japanese Patent Application Laid-Open No. H10-195360). On the other hand, a microcapsule type pigment having a pigment coated with a resin has also been proposed (e.g., Japanese Patent Application Laid-Open Nos. H08-183920 and 2003-34770). Especially, Japanese Patent Application Laid-Open No. 2003-34770 discloses an aqueous colored fine-particle dispersion comprising a water-insoluble coloring agent which is prepared by dispersing a water-insoluble coloring agent in an aqueous medium in the presence of a dispersant and then adding a vinyl monomer and polymerizing it, and which shows dispersion stability when dispersing the water-insoluble coloring agent, while the stability of the resultant latex is poor when polymerizing the vinyl monomer in the presence of only the dispersant, and describes “when emulsion-polymerized into the water-insoluble coloring agent dispersion, because the affinity of the dispersant with the vinyl monomer and resulting polymer is not so high with the result that the dispersant is difficult to be desorbed from the pigment particle surfaces and the polymerization proceeds on the dispersant-adsorbed pigment particle surfaces, the pigment-surface-coated, fine-particle dispersion can be obtained with a high yield without causing agglomeration, and further describes that by using the colored fine-particle dispersion, an aqueous ink is obtained, which is excellent in dispersion stability and printing characteristics, shows little metallic gloss, has no dependency on the paper type, and gives an image excellent in waterfastness, lightfastness and rubfastness.
However, there have been cases where these techniques do not provide dispersion stability of a colorant and gross of a recorded image sufficiently. The present inventors have made extensive study and considered that in order to improve the dispersion stability, it is necessary to increase the density of functional groups on the surface of a colorant. However, in the conventional technique using a polymeric dispersant and the technique disclosed by Japanese Patent Application Laid-Open No. H08-183920 using a resin-coated pigment, there were cases where when the acid value of a resin was increased in order to improve the dispersion stability, the hydrophilicity of the resin also increased and the resin became liable to be separated from the colorant with the elapse of time, so that the storage stability could not be maintained for a long period of time. On the other hand, with the technique of chemically modifying the surface of a water-insoluble colorant as disclosed by Japanese Patent Application Laid-Open No. H10-195360, there have been posed the problems that the modifiable functional groups and the density thereof are limited, and that effecting direct chemical modification, particularly when the colorant is an organic pigment, will cause the so-called “pigment exfoliation” in which pigment molecules, which are originally water-insoluble and crystallized, become water-soluble through bonding of hydrophilic groups to be dissolved out from pigment particles, thereby significantly change the hue (see FIGS. 6A and 6B). Therefore, these conventional techniques are not fully developed to sufficiently satisfy the recent requirements.